Christmas multicolored light strings are widely used for decoration during many special holidays. They are most often seen on christmas trees which are decorated together with other ornaments.
In general, the sockets of the light strings are electrically connected in series so that the disconnection of even only one bulb breaks the electrical circuit and renders the entire light strings to fail. Therefore, an effective and secured fastening structure for retaining a bulb in a socket is urgently required.
As shown in FIG. 6, a conventional bulb and socket device in christmas light strings, for example disclosed in U.S. Pat. No. 4,943,899, generally includes a bulb 60 and a socket 70. The bulb 60 includes a lighting element 61, an inserting base 62 having two leads 621 oppositely mounted on two sides thereof, and two tongues 63 which extends outward from two upper sides of the base 62 respectively. Each tongue 63 has a slot 631 formed adjacent to a free end thereof. The socket 70 has two T-shaped male members 71 oppositely formed and adjacent to the top margin thereon. The inserting base 62 is retainable within a central hole 72 of the socket 70 and the leads 621 are contactable onto an unshown electrical circuit. The bulb 60 is further fastened to the socket 70 by bending each tongue 63 downward and pushing the tongue 63 against the T-shaped male member 71 so that a snapping head 711 formed on the T-shaped male member 71 is forced through the slot 631.
The tightening ability of the abovementioned structure is based on the deformable strength of the tongue 63 itself and the retaining force exerted on the tongue 63 through the retained slot 631 by the snapping head 711 of the T-shaped male member 71. The severe defect in such design is that the tongue 63 is quite often broken apart resulting from possibly repeated or accidental bending during manufacturing or assembling the light strings.